The proposed research addresses research topic #22: Animal Models of Aging. In an effort to determine whether gorillas may serve as a suitable model for the physiological processes associated with menopause, we propose a pilot study to investigate reproductive senescence in western lowland gorillas. More specifically, we will evaluate the following questions: (1) Do gorillas undergo physiological cessation of ovulation at advanced age? We will assess levels of estrogen and progesterone from fecal and urine samples in order to determine if hormonal patterns are consistent with normal ovulatory function, or are indicative of irregular or inadequate ovarian function. (2) Are behavioral patterns associated with reproduction linked to hormonal changes? We will use standard observational sampling methods (Altmann, 1974) to collect simultaneous behavioral and hormonal data on geriatric and non-geriatric gorillas to determine whether pronounced episodes of proceptive behavior parallel, or are independent of, hormonal patterns. (3) Do aging gorilla females exhibit health-related problems similar to those experienced by menopausal human females? Aging gorillas are known to experience osteoarthritis, cardiovascular disease, and neurological degeneration. We will evaluate whether occurrence of these disorders is associated with declines in estrogen consistent with menopausal symptoms. We will review pathology reports for deaths of sexually mature female gorillas to evaluate the extent to which typical age-related, and hormonal-related, disease associations are prevalent in this population. (4) Given their close evolutionary ties to Homo sapiens, do gorillas represent a new model for longitudinal studies on the consequences of aging and reproductive senescence? Depending on the findings of (1) through (3), above, we will evaluate the efficacy of utilizing retrospective and prospective data from the captive gorilla population as a model for the physiological processes associated with the human menopause. We will collect concurrent behavioral and hormonal data on a minimum of 16 geriatric females and 6-11 prime-age control females to determine the extent to which these aging females differ from prime-age females in proceptive behavior and ovulatory patterns, and to evaluate whether the patterns are consistent with menopause. Given the current state of the captive gorilla population (roughly 30% of females are considered to be geriatric), this research is timely.